This invention relates to the production of hollow concrete cylinders in which the concrete forming the cylinder is maintained under stress by high tensile strength steel wires or strands sometimes called tendons.
It is usual to form the cylinder and subsequently to fit a tendon in wrap around fashion under stress onto the outer surface. The tendon is then fixed and encased in grouting material such as gunite. Other systems are known in which the tendons are at least partially enclosed in the parent concrete of the cylinder, however, total enclosure is not possible and furthermore, these systems suffer because of their complexity.
It is a principal objective of the present invention to provide a stressed hollow concrete cylinder in which the stressing medium is totally enclosed by concrete which forms the cylinder whole.